Memory in the pensieve, a man yelling at a cowering woman and child. Most people assume that this was Tobias Snape versus Eileen and young Severus. I prefer the theory that the man was Grandad Prince because it fits with Marvolo versus Merope. Also if Tobias and Eileen had an abusive relationship, I don't see why Severus would have been so happy to take the nickname "Half blood Prince".